Thousands of children and adults in the U.S. suffer from upper-limb deficiencies. Current state-of-the-art prehensors intended to increase upper-limb function do not serve this population well. This Phase II SBIR project addresses that situation by focusing upon optimizing a body-powered voluntary-closing (VC) prehensor offering variable mechanical advantage (VMA) and passive holding-assist. Extensive Phase I laboratory testing and field trials with amputee volunteers has established the devices technical feasibility and potential cost-effectiveness. The overall goal of this multi-phase project is to make a next-generation prehensor available to individuals of all ages for whom existing devices are unsuitable or otherwise unsatisfactory. Practical VC prehensors have long been desired for their natural and intuitive operation that promotes proprioception. However, engineering difficulties have prevented the realization of such designs. The device being developed under this project overcomes those technical barriers. In Phase II, units for adult and child use will be designed and fabricated. They will incorporate the comprehensive feedback from experts, amputees, and prosthetists obtained during Phases I and II. Manufacturing processes will be established, and extensive testing and volunteer field trials will be carried out to confirm that the devices perform as required. Educational user materials will also be prepared and evaluated. PROPOSED COMMERCIAL APPLICATION: The LESA Prehensor represents a new terminal device that will be routinely prescribed by prosthetic clinicians in the construction of assistive application.